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Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe |
Date: |
Mon, 24 Oct 2011 10:54:52 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:7.0) Gecko/20110927 Thunderbird/7.0 |
Am 24.10.2011 10:47, schrieb Paolo Bonzini:
> On 10/24/2011 10:17 AM, Kevin Wolf wrote:
>>> I think it's not about "why is it there", but rather about "what is it
>>> useful for". My interpretation of it is "I do not need the image
>>> anymore unless the command exits cleanly": VM installations, qemu-img
>>> conversions, BDRV_O_SNAPSHOT (doesn't do it yet, but it could). Even
>>> SIGINT and SIGTERM would be excluded from this definition, but they cost
>>> nothing so it's nice to include them.
>>
>> I think another common interpretation is: "I don't run this VM in
>> production but for development. I want the VM to go faster and I can
>> recreate the image in the unlikely event that power fails during my
>> work. But it certainly would be nasty."
>
> Fair enough.
>
>> But I think that starting to make exceptions for single block drivers
>> isn't a good idea anyway. If we want bdrv_flush() to write out all
>> metadata internal to qemu, I think the approach with checking the flag
>> in drivers calling things like fsync() is better. The common thing is to
>> do the flush.
>
> I don't know... checking BDRV_O_NO_FLUSH in the drivers rather than in
> the generic code sounds like a layering violation. Perhaps what you're
> after is a separation of bdrv_co_flush from bdrv_{,co_,aio_}fsync? Then
> BDRV_O_NO_FLUSH (better renamed to BDRV_O_NO_FSYNC...) would only
> inhibit the latter.
Why? All other cache related BDRV_O_* flags are interpreted by the block
drivers, so why should BDRV_O_NO_FLUSH be special?
Kevin
- [Qemu-devel] [PATCH 2/2] block: Handle cache=unsafe only in raw-posix/win32, (continued)
- [Qemu-devel] [PATCH 2/2] block: Handle cache=unsafe only in raw-posix/win32, Kevin Wolf, 2011/10/21
- [Qemu-devel] [PATCH 1/2] raw-posix: Convert to bdrv_co_flush, Kevin Wolf, 2011/10/21
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Paolo Bonzini, 2011/10/21
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Kevin Wolf, 2011/10/24
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Paolo Bonzini, 2011/10/24
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Kevin Wolf, 2011/10/24
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Paolo Bonzini, 2011/10/24
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe,
Kevin Wolf <=
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Paolo Bonzini, 2011/10/24
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Kevin Wolf, 2011/10/24
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Paolo Bonzini, 2011/10/24
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Kevin Wolf, 2011/10/24
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Paolo Bonzini, 2011/10/24
- Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe, Peter Maydell, 2011/10/24